There have been continuing improvements in the well-known fluid catalytic cracking (FCC) process since its commercialization in the 1940s. Typically, a hydrocarbon feedstock was introduced into a lower portion of a vertically extending conduit along with hot regenerated catalyst from a catalyst regenerator and the mixture passed upwardly into a reactor. Up until the mid-1970s, the typical feed system for a fluid catalytic cracking unit consisted of a four-or six-inch diameter feed pipe inserted into the center of the vertical or sloped riser. The feed pipe extended into the bottom of the riser to a point that was typically between the center line of the riser and the top of the intersection of the regenerated catalyst standpipe and the riser. Such feed systems also relied on the vaporization of the feed to provide the major fluidizing media for the catalyst and to move the catalyst from the bottom of the hot regenerated catalyst standpipe to the top of the riser.
Of course, there were other systems, such as those that had feed distributors/nozzles around the circumference of the riser. Normally these systems were built in such a manner for mechanical reasons, since the regenerated catalyst was moved through a U-bend or J-bend in a dense phase before it was contacted with the hydrocarbon feedstock at the bottom of the riser.
The main drawback to such systems was that either the feedstock was in the center and the catalyst concentrated in the annular area of the riser, or the feed was injected around the circumference of the riser and the catalyst concentrated in the center. These systems resulted in very poor distribution of the catalyst and oil so that some oil molecules would see high catalyst to oil ratios, and high temperatures, and other oil molecules would see low catalyst to oil ratios and temperatures. That is, some of the oil would be overcracked and other oil would be hardly converted at all.
In the early to mid 1970s, the FCC unit (FCCU) design went through a series of rapid changes. This period saw the modification of FCCU's to riser cracking and to complete combustion in the FCCU regenerators. Also, the FCC catalyst was rapidly changing over to zeolytic type catalysts, and the push was on to effectively feed residual oil to the FCCU. One of the results of these changes was to put more emphasis on the method of feed injection into the riser and the method of mixing/contacting the feed and regenerated catalyst. Numerous patents have been issued concerning the subject of the proper method and apparatus for injecting feed into the riser. One of the early patents was my U.S. Pat. No. 4,097,243, issued Jun. 27, 1978 and entitled "Hydrocarbon Feed Distributor For Injecting Hydrocarbon Feed", which discloses the use of a hydrocarbon feedstock distributor in the lower end of a riser reactor. Another patent of import is DEAN's May 25, 1982 U.S. Pat. No. 4,331,533, entitled "Method and Apparatus for Cracking Residual Oils", which discusses the necessity for injecting the feed correctly into the lower part of the riser. Since the Dean patent, the theory that feed atomization was the key to better yields in fluidized catalytic cracking has been universally accepted in the industry. This quest for better feed atomization has resulted in increasing the pressure drop across feed distributors to as high as 150-200 psi, so that small particle droplets of feed (less than 100 microns) are formed.
A primary object of the present invention is an improved method of contacting a hydrocarbon feedstock with a particulate solid in a contacting zone of a fluidized system for processing hydrocarbon feedstocks. Other objects and advantages of the present invention will become apparent from the following description and the practice of the present invention.